function doppler = fd(p_i_s, s, v_i_s, f_c)
%FD 计算多普勒理论值
%   此处显示详细说明
    n = length(p_i_s);
    env = enviroment;
    satpos = p_i_s;
    satvel = v_i_s;
    ini_pos_temp = s(1:3);
    ini_vel_temp = s(4:6);
    
    V = (satvel-ini_vel_temp);
    P = (satpos-ini_pos_temp);
    R = vecnorm(P')';
env = enviroment;
% doppler = -sum(V.*(P./R),2)*f_c/env.c-s(7)*f_c*ones(n,1);
% doppler = -sum(V.*(P./R),2)*f_c/env.c;
doppler = -sum(V.*(P./R),2)*f_c/env.c-s(7);
end

